The present invention relates to a scroll type fluid machine for use as a compressor, an expander or the like.
A scroll type compressor according to the prior art is shown in FIGS. 3A and 3B.
In FIGS. 3A and 3B, reference numeral 1 denotes a stationary scroll which is composed of an end plate 1a and a spiral wrap 1b raised from an inner surface of the end plate 1a. Reference numeral 2 denotes a swivel scroll which is composed of an end plate 2a and a spiral wrap 2b raised from an inner surface of the end plate 2a in substantially the same shape of that of the above-described spiral wrap 1b.
The stationary scroll 1 and swivel scroll 2 are displaced by a predetermined distance r between their centers O.sub.1 and O.sub.2, and their phase is displaced by 180.degree. to obtain the engagement combination shown, whereby a plurality of compression chambers 3 are defined about the center of the spiral shape with a point symmetry.
A cylindrical boss 4 is projected from an outer central portion of the end plate 2a of the swivel scroll 2. A drive bush 5 is rotatably engaged within the boss 4 through a bearing 6. A slide hole 7 is formed in the drive bush 5. An eccentric pin, which eccentrically projects by a predetermined distance r from the axial center O.sub.1 of an end face of a rotary shaft 8, is engaged within this slide hole 7.
As shown in FIG. 3B, a cross section of the slide hole 7 is in the form of an oblong shape slanted by an angle .theta. relative to the eccentric direction of the eccentric pin 9. Linear portions 9a formed by cutting both sides of the eccentric pin 9 may slide in contact with and along linear portions 7a of the slide hole 7.
When the rotary shaft 8 is rotated, its rotational torque is transmitted to the drive bush 5 through the linear portion 7a of the slide hole 7 from the linear portions 9a of the eccentric pin 9 and is further transmitted to the swivel scroll 2 through the bearing 6 and the boss 4.
Thus, the swivel scroll 2 is orbited and swivelled on a circular locus having a radius of a predetermined distance r about a center O.sub.1 of the axis of the rotary shaft 8 under the condition that the swivel scroll 2 is prevented from rotating about its own axis by a revolving preventing mechanism (not shown).
Then, as gas entrained within the compression chambers 3 is moved toward the center of the spiral shape while reducing their volume, the gas is gradually compressed to reach the central chamber 11 and is discharged through the outlet port 12.
In accordance with the orbiting swivelling motion of the swivel scroll 2, a centrifugal force Fs which is directed in the eccentric direction of the eccentric pin 9 is generated by a weight imbalance caused by the swivel scroll 2, the boss 4, the bearing 6, the drive bush 5 and the like.
On the other hand, a gas force Fp is applied to the swivel scroll by the gas pressure within the compression chambers 3.
The drive bush 5 is moved in the direction of the angle .theta. by a component F of the centrifugal force Fs and the gas pressure Fp in the direction of the angle .theta. so that the orbiting and swivelling radius of the swivel scroll 2 is increased, and side surfaces of the spiral wrap 2b of the swivel scroll 2 are pressed on side surfaces of the spiral wrap 1b of the stationary scroll 1 by the above-described force F.
In the above-described scroll type compressor, there is a fear that when the centrifugal force Fs is increased by the increase of the orbiting swivelling speed of the swivel scroll 2, the force for pressing the side surfaces of the spiral wrap 2b of the swivel scroll 2 against the side surfaces of the spiral wrap 1b of the stationary scroll 1 would be so excessive that the side surfaces of the spiral wraps 1b and 2b would be abnormally worn out.
When the orbiting swivelling speed of the swivel scroll exceeds a predetermined level, the swivel scroll is moved in a direction so that the orbiting swivelling radius is decreased. Accordingly, it is possible to suppress the extra contact pressure between the spiral wrap of the swivel scroll and the spiral wrap of the stationary scroll.